Technical Field
The present invention relates to a technique for measuring specimens using light.
Background Art
In recent years, Optical Coherence Tomography, which acquires using light images in which surficial structures or internal structures of specimen are reflected, is drawing attentions. Since OCT is not invasive to human bodies, it is expected to be applied to medical fields and biological fields. With regard to ophthalmology fields, devices that form images of ocular fundus or cornea are in practical use. In OCT measurement, light from optical source is divided into signal light and reference light, the signal light acquired by irradiating the light onto the specimen and the reference light acquired by reflecting the light with reference light mirror without irradiating onto the specimen. The signal light reflected from the specimen is multiplexed with the reference light, thereby causing interference with each other to acquire detection signals.
OCT is generally categorized into time domain OCT and Fourier domain OCT depending on the scanning method in the optical axis direction at the measurement position. In time domain OCT, low coherence light source is used as the light source. Scanning is performed in the optical axis direction by scanning the reference light mirror during measurement. Then only the components in the signal light which optical path length is identical to that of the reference light interfere. Signals are demodulated by performing envelope demodulation to the acquired interference signals. On the other hand, Fourier domain OCT is further categorized into swept source OCT and spectrum domain OCT. In swept source OCT, swept source optical source is used that is capable of scanning the wavelength of the emitted light. Scanning in the optical axis direction is performed by scanning the wavelength during measurement. Signals are demodulated by performing Fourier conversion to wavelength dependency (interference spectrum) of the detected interference light intensity. In spectrum domain OCT, broadband light source is used. The generated interference light is dispersed by spectroscope. Scanning in the optical axis direction corresponds to detecting interference light intensity (interference spectrum) for each wavelength component. Signals are demodulated by performing Fourier conversion to the acquired interference spectrum.
Patent Document 1 listed below describes a technique in which the objective lens is physically scanned and in which four detectors each having different phase conditions receive interferences between signal light and interference light, thereby eliminating the need for adjusting phases of reference light by scanning mirrors in time domain OCT.
Patent Document 2 listed below describes a technique that measures, applying scatter angle distribution of protein sample and particle tracking with microscope observation, particle size distribution of sample in conjunction with measurement result of positional disturbance due to Brownian motion.